Medical balloon

ABSTRACT

A medical balloon for a balloon catheter is described. The balloon has at least a first layer made from a first material and a second layer made from a second material, said first and second layers being in overlying relationship with one another and being integral with one another; wherein the first layer has a softening or melting temperature which is higher than a softening or melting temperature of the second layer. A method of forming the medical balloon is also described, including locating a raw tubing in a mold; preheating and inflating the raw tubing so as to cause it to stretch; heating the raw tubing to soften or melt the second layer; setting the inflated raw tubing to form the medical balloon; and cooling the set balloon.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a Continuation under 35 U.S.C. § 120 of U.S. patentapplication Ser. No. 13/794,972, filed Mar. 12, 2013, which claimspriority to GB application no. 1205369.0, filed Mar. 27, 2012, titled“Method of Making a Medical Balloon,” the contents of each of which areincorporated herein by reference in their entirety.

TECHNICAL FIELD

The present invention relates to a method of making a medical balloon,to a medical balloon and to a balloon catheter including such a balloon.

BACKGROUND ART

Medical balloons are used for a variety of medical procedures includingangioplasty, scoring, vessel dilatation, valvuloplasty, occlusion, andfor many other applications. In many such applications, it is desirableto provide additional components to tailor the balloon to improve itsfunction in each of the various specific uses. One common procedureinvolving the use of a balloon catheter relates to angioplasty dilationof coronary or other arteries suffering from stenosis (that is, anarrowing of the arterial lumen which restricts blood flow). Inangioplasty techniques the proper dilation of stenosed regions that arehardened and/or have become calcified can be difficult with a standardmedical balloon. Therefore it is known to fix cutting elements, such asblades, onto the surface of the balloon in order to cut away at plaqueand other build-up on the interior walls of a lumen. The blades may befixed to the balloon with a layer of adhesive in a process can be fiddlyand time consuming.

Often the manufacture of medical balloons is a complex and timeconsuming task, particularly having regard to the importance forreliability of the device.

Medical balloons are disclosed in a number of earlier publicationsincluding, for example, in US 2010/0036314, U.S. Pat. No. 6,143,416,U.S. Pat. No. 6,786,889, US 2009/0299450, U.S. Pat. No. 5,620,649, U.S.Pat. No. 7,828,766 and US 2010/0262218.

DISCLOSURE OF THE INVENTION

The present invention seeks to provide an improved method of making amedical balloon and an improved medical balloon and balloon catheter.

According to an aspect of the present invention there is provided amethod of forming a medical balloon provided with a first layer madefrom a first material and a second layer made from a second material,said first and second layers being in overlying relationship with oneanother and integral with one another, wherein the first material has asoftening or melting temperature which is higher than a softening ormelting temperature of the second material; the method including thesteps of: providing first and second layers of raw tubing made of saidfirst and second materials respectively; locating said raw tubing in amold; preheating the raw tubing to a preheat temperature and inflatingthe raw tubing so as to cause it to expand; heating the raw tubing to afirst heat set temperature being the heat set temperature of the firstlayer and greater than the heat set temperature of the second layer,wherein at said preheat temperature the second layer is softened ormolten, and/or wherein at said first heat set temperature the secondlayer is softened or molten, and/or wherein in the range between theheat set temperature and the preheat temperature the second layer issoftened or molten; setting the inflated raw tubing to form the medicalballoon; and cooling the set balloon.

In preferred embodiments the second layer is molten at the preheattemperature and/or at the first heat set temperature and/or in the rangebetween the heat set temperature and the preheat temperature.

The method may include the step of incorporating a feature or componentinto the second layer. For example the method may comprise the step ofapplying texture to the second layer, in particular to an outer surfaceof the second layer.

The method may include the steps of providing adjacent the second layerat least one component and pressing the at least one component into thesecond layer such that the at least one component becomes at leastpartially embedded in the second layer. The at least one component maybecome fully embedded in the second layer.

Preferably the method provides a single stage process for forming amedical balloon, in particular for incorporating a feature or componentinto a medical balloon. The process can be faster and simpler than knownmethods for producing medical balloons.

The raw tubing may be a single tube having first and second layersintegral with one another. The raw tubing may comprise two separate rawtubing layers. The two separate raw tubing layers may be held closelyadjacent to one another. The second layer may be an outer layer of theraw tubing. The first layer may be an inner layer of the raw tubing.

The preheating step may heat the raw tubing to around 100 degreescentigrade.

The first heat set temperature may be in the region of 130 to 150degrees centigrade. The first heat set temperature may be in the regionof 140 to 150 degrees centigrade. The first heat set temperature may bethe optimum heat set temperature of the first material.

According to another aspect of the present invention, there is provideda medical balloon for a balloon catheter, which balloon has at least afirst layer made from a first material and a second layer made from asecond material, said first and second layers being in overlyingrelationship with one another and being integral with one another;wherein the first layer has a softening or melting temperature which ishigher than a softening or melting temperature of the second layer.

The first layer may act as a support for the second layer. The firstlayer may support the second layer at all times, even during manufactureof the balloon from raw tubing. By provision of the supporting firstlayer the balloon can be adapted to include an additional feature orcomponent in the second layer without compromising the physicalcharacteristics of the balloon, such as its strength or integrity. Evenif the second layer loses strength or integrity, for example duringmanufacture, the balloon can maintain the characteristics required toperform its function by virtue of the presence of the first layer.

The first layer may be made from polyamide, polyether block amide,polyurethane, polyethylene, polyethylene terephthalate (PET) orsilicone. The polyamide may be Nylon. The polyether block amide may bePEBAX™. The second layer may be made from the same material as the firstlayer, treated to have a lower softening or melting temperature thanthat of the first layer. The second layer may be made from any materialhaving a lower melting temperature than the first layer. For example thesecond layer may be made from a resin, such as a functionalizedpolyolefin resin or a polyurethane resin. Examples of suitable materialsfor the second layer include an anhydride-modified ethylene elastomerbased adhesive resin (such as Admer® SF755A), an anhydride-modifiedlinear low density polyethylene (such as Plexar® PX3236 or a polyolefinmodified with functional chemical groups to render it more hydrophilic.The second layer may be an amorphous polymer. In an embodiment thesecond layer is non-elastomeric. In an embodiment, both layers arethermoplastic elastomers. The inner layer may be a polyurethane that maybe unmodified. The outer layer may be a polyolefin, which may bemodified with hydroxyl groups or modified with anhydride groups.

The second layer may be softened or melted at or above a preheat orfirst processing temperature of the first layer. By preheat or firstprocessing temperature it is meant a temperature at which the firstlayer can be stretched. The preheat or first processing temperature maybe the temperature to which the balloon is heated to in a preheat step.The preheat or first processing temperature may be, for example, 100degrees centigrade. The melting temperature of the second layer may beunder 100° C., under 120° C. or under 140° C. The preferred meltingtemperature of the second layer may be in the range of 115 to 125degrees centigrade. In an embodiment, the melting temperature of thefirst layer may be in the range of about 165 to about 205 degreescentigrade.

The first layer may have a heat set temperature above which the firstlayer is heat set. The second layer may have a heat set temperatureabove which the second material is heat set. The second layer may have aheat set temperature which is less that the heat set temperature of thefirst layer. When a material is heated to its heat set temperaturewhilst it is stretched, for example by inflation of the balloon, thematerial becomes fixed such that when inflation pressure is removed fromthe balloon the material maintains its size and form, rather thanreturning to its pre-inflated size and form. It is believed that at theheat set temperature the molecules of the material are substantiallylocked into their orientations such that on cooling the molecules do notreturn to any orientation they may have had before heat setting.

A balloon may be stretched and heated below the heat set temperature andon cooling may return, or at least partially return, to itspre-stretched and pre heated form. Heating a material to its heat settemperature may reduce, in particular minimize, shrinkage of the balloonon cooling after heating. Heating a balloon material to its heat settemperature may also increase the burst strength of the balloon. Heatinga balloon material to a temperature above its heat set temperature mayresult in loss of burst strength compared to the burst strength of theballoon after heating only to its heat set temperature and then cooling.Heating a material to a temperature higher than its heat set temperaturemay over-heat the material. By over-heating the balloon material it maylose at least some of its strength, possibly as a result in breakage ofthe polymer chains of the material. For example the second layer maylose its burst strength by heating it to the heat-set temperature of thefirst layer.

The first layer may have a heat set temperature between around 130 to150 degrees centigrade, 140 to 150 degrees centigrade, or 145 to 150degrees centigrade. The heat set temperature of the outer layer may beless than about 140 degrees centigrade. In embodiments it may be lessthan about 100 degrees centigrade. The second layer may have a heat settemperature of around 55 to 70 degrees centigrade. The second layer mayhave a heat set temperature of around 50 to 60 degrees centigrade. Thesecond layer may have a heat set temperature which is at least 80, 70,60, 50, 40 or 30 degrees centigrade less than the heat set temperatureof the first layer. The second layer may have a heat set temperaturewhich is at least 20 degrees centigrade less than the heat settemperature of the first layer. The second layer may have a heat settemperature which is at least 10 degrees centigrade less than the heatset temperature of the first layer. The second layer may have a heat settemperature which is no more than around 80% of the heat set temperatureof the first layer.

Where the heat set temperature is a temperature range, the first layermay have an optimum heat set temperature within the heat set temperaturerange. Heating the balloon to the optimum heat set temperature of thefirst layer may result in a balloon for which shrinkage is minimized andburst strength is maximized.

Due to the relative hardness of the two layers, the first layer mayprovide a harder support for the second layer.

The first layer may have a thickness in the range from 0.01 millimetersto 0.05 millimeters. The first layer may have a thickness in the rangefrom 0.02 millimeters to 0.04 millimeters. The second layer may have athickness in the range from 0.003 millimeters to 0.02 millimeters. Thesecond layer may have a thickness which is no more than 20% of athickness of the first layer. The second layer may have a thicknesswhich is no more than 40% of a thickness of the first layer.

In embodiments the thickness of the second layer may be equal to thethickness of the first layer. For example the second layer may have athickness in the range from 0.01 millimeters to 0.05 millimeters. Inother embodiments the thickness of the second layer may be greater thanthe thickness of the first layer. For example the second layer may havea thickness of up to 0.2 mm. A thicker second layer may be provided soas to enable elements to be at least partially embedded into the secondlayer.

The thickness of the first layer of the balloon may be chosen so as toprovide the desired physical characteristics of the balloon. Thephysical characteristics of the balloon, such as burst strength,compliance and shape may be substantially determined by the first layer.The second layer may have no significant influence on suchcharacteristics of the balloon. The first layer of the balloon may havea thickness equal to that of a single layer balloon exhibiting thedesired physical characteristics of the balloon.

Preferably the burst strength of the inner layer is higher than theburst strength of outer layer.

The medical balloon may include at least one feature or component in thesecond layer. The second layer preferably has sufficient thickness suchthat an additional component may be securely embedded in the secondlayer, or sufficient thickness such that an additional feature may beprovided in the second layer. An additional component may be partiallyor completely embedded in the second layer. The second layer may berelatively thick, for example it may be thicker than adhesive layerswhich have been used to bind additional components to balloons inexisting products. As such additional components may be incorporatedinto a balloon of a balloon catheter more securely and more easily.

The first layer may be an inner layer and the second layer may be theouter layer of the balloon. The medical balloon may include at least oneother layer integral with the first and second layers, the second layerbeing an outer layer of the balloon.

The medical balloon may include at least one component at leastpartially embedded in the second layer. The component may be or mayinclude a strengthening sleeve, a woven material, a scoring element, aburst resist wire, a radiopaque marker, a cutting element, a highfriction element, or a texturizing element. A texturizing element mayfor example be roughening particles which, when incorporated into thesecond layer, provide a roughened surface of the second layer. Theadditional component may tailor the features of the balloon, for exampleto improve the balloon's performance for a specific use. The additionalcomponent may be integral with the second layer of the balloon forexample by being embedded in or incorporated into the second layer. Theadditional component may protrude beyond the surface of the second layerof the balloon, for example to provide a scoring surface.

The second layer may comprise a soft layer. By soft it is meant that thelayer may deform around an element or device, such as a stent, pressedinto it. The second layer may remain relatively soft after manufactureof the balloon such that an element or device may be partially embeddedinto the soft layer after manufacture of the balloon. For example, astent may be crimped into the soft layer in order to attach it to theballoon. In this case the stent may be partially embedded in the softlayer. Where the second layer is a soft layer the second layer may bethicker than the first layer.

The second layer may comprise a high friction layer. For example thesecond layer may comprise a material which gives the surface of thesecond layer high friction.

The medical balloon may include at least one feature in the outer layer.For example the outer layer may be textured, such as roughened, or theouter layer may be a high friction layer.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the present invention are described below, by way ofexample only, with reference to the accompanying drawings, in which:

FIG. 1 is a schematic diagram of a balloon catheter;

FIG. 2 is a cross-sectional sectional view of an embodiment of themedical balloon taught herein;

FIG. 3 is a cross-sectional view along Y-Y of the medical balloon ofFIG. 2;

FIG. 4 is a cross-sectional sectional view of another embodiment of themedical balloon;

FIG. 5 is a cross-sectional view of yet another embodiment of themedical balloon;

FIG. 6 is a schematic view of an embodiment of assembly for use in themanufacture of medical balloon and balloon catheters of the typesdisclosed herein;

FIG. 7 is a cross-sectional view of an embodiment of the raw tubing fora medical balloon positioned inside a mold, for manufacturing a medicalballoon as taught herein;

FIG. 8 is a cross-sectional view along X-X of the raw tubing and mold ofFIG. 7; and

FIG. 9 is a graph depicting the shrinkage and burst strength of theinner and outer layers of balloon material as they vary withtemperature.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

It is to be understood that the drawings are schematic only and are notintended to be representative of dimensions or proportions of thevarious elements shown therein. In some instances, dimensions, sizes andproportions have been modified in order to assist in the visualizationof various features of the elements shown, that is for the purpose ofexplanation only. The person skilled in the art will be aware of theappropriate dimensions and proportions having regard to common knowledgein the art.

Referring to FIG. 1, there is shown in schematic form the principalcomponents of a balloon catheter assembly 10, which components aregenerally known in the art. The balloon catheter includes a catheter 12having a proximal end 14 and a distal end 16. At the proximal end 14,the catheter is coupled to a manipulation unit and valve assembly 18,which typically includes one or more haemostatic valves (not shown), aport 20 for feeding flushing liquid into the catheter 12, typicallysaline solution, and a proximal cannula 22 for use, for example, infeeding a guide wire (not shown) through the catheter 12.

At the distal end 16 of the balloon catheter 10, there is provided amedical balloon 24. The balloon 24 may be used, for example, in anangioplasty or other vessel dilatation procedure, for valvuloplasty, forocclusion, or for any other procedure. The balloon 24 is typicallywrappable around the catheter 12, the latter extending through theballoon 24 to the tip 26 of the assembly 10. The balloon is alsoinflatable, via an inflation lumen in the catheter 12, so as to attain adeployed, inflated configuration, as shown in FIG. 1. The balloon 24 mayhave a variety of shapes but typically may have a substantiallycylindrical body portion bounded by conical end portions whichthemselves are bounded to neck portions which are fixed in fluid tightmanner to the catheter 12.

Referring now to FIGS. 2 and 3, there is shown a first embodiment ofmedical balloon 30 according to the teachings herein. The balloon 30 hasa strengthening element 44 for strengthening the balloon. FIG. 2 iscross sectional view of a part of the balloon 30 taken along thelongitudinal axis of the balloon. FIG. 3, on the other hand, is a viewof the balloon 30 along its longitudinal axis. The balloon 30 has a bodyportion 32 which is substantially cylindrical. This is bounded by firstand second conical ends 34 which in turn terminate at first and secondnecks 36 which are typically bonded or otherwise sealed to a catheter50. It will be apparent, in particular from FIG. 2, that catheter 50extends through the balloon 30 and is provided, typically, with aninflation lumen 52 which has a port 54 in communication with theinternal chamber 38 of the balloon 30. Inflation lumen 52 is used toinflate and deflate the balloon 30 for deployment purposes, in a mannerwell known in the art.

As can be seen in FIG. 2, the balloon 30 is formed, of an inner layer 40and an outer layer 42. Typically, the inner and outer layers 40, 42 havea substantially even thickness, although it is not excluded that theymay have a non-uniform thickness. The outer layer is thick compared to,for example, a layer of adhesive, which may alternatively be used tobind an additional component to a balloon. The end cones 34 and/or thenecks 36 may have a thickness which varies, for example as a result ofthe method of manufacture of the balloon.

The outer layer 42 is integral with or otherwise bonded to the innerlayer 40. The structure of layers 40, 42 is such that when the balloon30 is inflated, by means of inflation fluid fed through the lumen 54 ofthe catheter 50, the balloon 30 will unwrap from the catheter 50 andexpand to its inflated condition shown in FIGS. 2 and 3.

The strengthening element 44 is fully embedded in the outer layer 42 ofthe balloon 30 such that it lies within the outer layer. Thestrengthening element may be embedded further into the balloon such thatit lies substantially between the inner 40 and outer 42 layers of theballoon 30. In another embodiment the strengthening element may bepartially embedded in the outer layer such that at least part of thestrengthening element protrudes from the second layer.

In a preferred embodiment the strengthening element is a strengtheningsleeve such as a braided or otherwise constructed mesh made fromfilamentary material. The filamentary material may be, for example, ametal wire. In one embodiment the strengthening element is astrengthening layer.

The inner layer 40 of the balloon 30 can be made of a variety ofmaterials including, for example, polyamide (e.g. Nylon), polyetherblock amide (e.g. PEBAX™), polyethylene, polyurethane, silicone,polyethylene terephthalate (PET) or other suitable material. The heatset temperature for Nylon and PEBAX™ may be approximately 140-145degrees centigrade. The outer layer 42 of the balloon could be made ofsimilar materials or a different material than that of the inner layer40, all being of a formulation having a lower softening or meltingtemperature than the material of the first balloon layer. The outerlayer 42 is preferably made of a functionalized polyolefin resin or apolyurethane resin. Of course, either or both layers 40, 42 can be madefrom a plurality of compounds. The outer layer 42 may be formed from apolyolefin base material modified with functional chemical groups tomake it more hydrophilic. Examples of suitable materials for the outerlayer include an anhydride-modified ethylene elastomer based adhesiveresin (such as Admer® SF755A) or an anhydride-modified linear lowdensity polyethylene (such as Plexar® PX3236).

In a preferred embodiment the physical characteristics of the balloon,such as burst strength, compliance and shape is substantially determinedby the inner layer. Preferably the outer layer has no significantinfluence on such characteristics of the balloon. Therefore, thethickness of the inner layer is preferably equal to the thickness of asingle layer balloon with the desired physical characteristics of themedical balloon. The inner layer provides a support for the outer layerat all stages of manufacture, allowing the properties andcharacteristics of the outer layer to change without compromising thephysical characteristics of the balloon.

The balloon could be non-compliant, semi-compliant or compliant independence upon the medical application. The compliance of the innerlayer 40 can be determined by a number of factors, including thematerial used, the nature of that material, the thicknesses of the layerand so on. These are all parameters which a person skilled in the artwill be able to ascertain on the basis of common general knowledge.

It is to be appreciated that the strengthening element 44 is just oneexample of an additional component or feature which may be incorporatedinto a medical balloon for use in medical procedures. The teachingsherein, particularly in connection with the method of manufacture of theballoon described below, allow for a large variety of differentadditional components to be incorporated into a medical balloon.

Some examples are given in FIGS. 4 and 5, to which reference is nowmade. All of these Figures show cross-sectional views of differentexamples of medical balloon.

In FIG. 4, a radiopaque element 74 is embedded so as to liesubstantially between the inner 70 and outer 72 layers of the balloon71. As with the previously described embodiments, the balloon 71includes inner and outer layers 70, 72 of the type disclosed herein. Theradiopaque element is made from radiopaque material such as, forexample, palladium, silver and other radiopaque materials known to theskilled person.

In a preferred embodiment the radiopaque element is a radiopaque layer.In other embodiments the radiopaque element maybe a radiopaquemarker-block.

As described previously with reference to other additional componentsincorporated into the balloon, in other embodiments the radiopaqueelement may be embedded within the outer layer so that it is surroundedby the outer layer, or partially embedded in the outer layer such thatit extends from the outer layer.

FIG. 5 shows a view of another example of a medical balloon 81 along itslongitudinal axis. The balloon 81 comprises a plurality of scoringelements 84 which extend longitudinally along the length of the balloon.The scoring elements, which may be thin wires or fibers 84, are stifferthan the balloon wall so that they can score into the wall of the vesselin which the balloon is inflated. The scoring elements may comprise aplastic polymer material, or a metal or metal alloy, such as Kevlar forexample. The scoring elements 84 are embedded in the outer layer 82 ofthe balloon 81 and protrude above the circular perimeter of the balloonso as to be able to interact with the wall of the lumen in which theballoon 81 is placed. In the embodiment shown in FIG. 5 the scoringelements 84 extend along the main body part of the balloon only, notalong the narrower end cone and neck portions of the balloon. Theballoon 80 has inner and outer layers 80, 82 of the characteristicstaught herein.

The additional components described with reference to the Figures couldbe used individually or in combination with one another. The componentsmay be arranged about any particular portion of the balloon, or aboutthe entire balloon.

The structure of the balloon and its method of manufacture, describedbelow, allows for the provision of medical balloons having a variety ofadditional components such that the specific characteristics of theballoon can be tailored for a particular medical application.

There follows a description of a preferred embodiment of manufacturing aballoon having characteristics of the type disclosed herein.

Referring now to FIG. 6, there is shown in schematic form an embodimentof assembly 100 for use in the manufacture of medical balloon andballoon catheters of the types disclosed herein.

The assembly 100 includes a mold 102, a pumping unit 104 for pumpinginflation fluid through a conduit 106 into the mold 102 and specificallyinto a raw tubing from which the medical balloon is formed as describedin further detail below. The pumping unit 104 may be provided with aheater 108 for heating the pumping fluid to various temperatures. Theremay be provided a separate heating unit 110 for heating the mold 102during the process of fabrication of a medical balloon.

In FIG. 7 there is shown a cross-sectional view of an embodiment of theraw tubing 131 for a medical balloon positioned inside a mold 112 shapedto produce a medical balloon having a strengthening element 134incorporated into it. FIG. 8 shows a cross-sectional view along X-X ofthe raw tubing and mold of FIG. 7. The mold 112 has an internal wall 114with a substantially cylindrical surface 116 bounded by taperingsections 118 which in practice will form the end cones 34 of theballoon.

A strengthening sleeve is located in the mold between the raw tubing andthe mold but not attached to either the mold or the tubing before theballoon is heated and expanded to incorporate the strengthening sleeve.

In the example of FIG. 7, the mold 112 is longitudinally divided in atleast two portions forming half a mold each. The structure of the mold112 is not, however, relevant to the disclosure herein in that the mold112 could have sections divided in other ways, for example transversallyrather than longitudinally, in order to gain access to the inside of themold for the purposes of removing a balloon formed therewithin.

Where the additional component is a strengthening wire, or a scoringelement, for example, longitudinal grooves (not shown) may be providedwithin the substantially cylindrical portion 116 of the mold in order toprovide a support for the strengthening wires or scoring elements. Thelongitudinal grooves may extend longitudinally along inside surface ofthe cylindrical portion 116. The grooves can support the additionalcomponents before they are incorporated into the outer layer of theballoon in the balloon forming process. In another embodiment theadditional components may be lightly attached to the mold or the tubingso as to support them in a desired position relative to the raw tubing131.

The raw tubing 131, of the type used in making a medical balloon of anyof the types disclosed herein, is located within the mold 112. The rawtubing 131 is formed, for example by co-extrusion, of two layers 130 and132. The inner layer 130 forms the inner layer 40, 70, 80 of theballoon, whereas the outer layer 132 forms the outer layer 42, 72, 82 ofthe balloon. These layers are thus made of the same material as theeventual layers of the balloon.

In practice, the raw tubing 131 is fed into the mold 12, typically inthe direction of the arrow 122 shown in FIG. 7 so as to extend into andthrough the mold 12. Once so fed, the raw tubing 131 is suitably clampedinto the mold and closed off at its extreme end. The fixing is such asto seal the end in fluid tight manner. This arrangement is known in theart and will thus be immediately evident to the skilled person.

The tubing 131, which is typically a very long or continuous length oftubing, is cut to an appropriate length and then coupled to the conduit106, in a known manner. In practice, the conduit 106 may form a ballooncatheter 12, in which case the raw tubing 131 would be fixed over thecatheter after having been cut to size with its two ends sealed to thecatheter 12 at locations which would form the necks 36 of the balloon.

The mold 112 is heated to a preheat temperature, such as, for example,100 degrees centigrade. Additionally, fluid pressure, typically alsoheated, is fed by means of the pump (104 shown in FIG. 6) into the rawtubing 131. The heat applied to the raw tubing causes the inner layer130 of the raw tubing to soften slightly and allows it to stretch whenthe pressure of the inflation fluid pushes against it, such that the rawtubing can expand within the chamber of the mold 112. The raw tubing 131is expanded towards the internal wall 114 of the mold 112, and the outerlayer 132 is eventually pressed against these walls and against thestrengthening element 134 by continuing inflation pressure.

Once the tubing 131 has been preheated and expanded to push against thewall 114 of the mold 112 the temperature of the mold 112 is increased soas to heat the inner layer 130 to its optimum heat set temperature.

At or above the preheat temperature the outer layer 132 of the balloonis softened more than the inner layer such that it is able to flow. Asthe outer layer 132 is able to flow, when the outer layer 132 is pushedagainst any additional component present in the mold the outer layer 132is displaced around said additional component and the additionalcomponent is forced into the outer layer 132. As the inner layer 130remains more solid and is not able to flow, the inner layer is notdisplaced around the additional component; the additional component doesnot to penetrate the inner layer.

The outer layer of the tubing may be displaced around the additionalcomponent to varying extents, for example, only slightly so as topartially embed the additional component in the surface of the outerlayer, or more substantially so as to fully embed the additional elementin the outer layer. The extent may depend on the thickness of the outerlayer, the thickness of the additional element, and the temperature towhich the tubing is heated in the preheat step. In the embodiment shownin FIGS. 7 and 8, where the additional component is a strengtheningelement, it is desired that the strengthening element be completelyembedded in the outer layer of the balloon.

Both the inner and outer layers 130,132 of the balloons are heat-set atthe heat set temperature of the inner layer. The inner layer is set soas to fix the bonds between the molecules in the expanded tubeconfiguration and to substantially prevent shrinkage on cooling. Theouter layer is also set so as to set the bonds between the molecules inthe expanded tube configuration.

FIG. 9 is a graph depicting the shrinkage of the inner 200 and outer 190layers and the burst strength of the inner 220 and outer 210 layers ofballoon material as they vary with temperature.

The graph shows that as temperature is increased to a materials heat settemperature (Heat set A and plot 220 for the inner layer and Heat set Band plot 210 for the outer layer) the burst strength of that materialrises, only to fall again on heating to above the heat set temperature.The graph also shows that as the temperature is increased above the heatset temperature the shrinkage of the balloon is dramatically reduced(when cooled after heating).

The graph also shows that once the material is heated to its heat settemperature, heating over that heat set temperature does not continue toreduce shrinkage on cooling. There is a preferred point therefore foreach material at the heat set temperature where shrinkage is minimizedand burst strength is maximized.

As can been seen from the graph, heating the outer layer to the heat settemperature of the inner layer, which heats the outer layer to atemperature above its own heat set temperature, results in a decrease inburst strength of the outer layer. This is possibly caused by breakageof the polymer chains of the material.

However, this does not compromise the strength or burst strength of theballoon as the inner layer maintains its strength and provides thephysical characteristics of the balloon.

Once the balloon has been heat set, the mold 112 is cooled or allowed tocool. On cooling the additional components are fixed into the outerlayer of the balloon and thus incorporated into the balloon. The mold112 is preferably cooled to substantially ambient temperature, and theballoon then removed from the mold. Typically, this can be achieved bydeflating the balloon so as to facilitate its retraction form the moldsurfaces.

The provision of two layers to the balloon integral with one anotherenables the reflow, molten or softened outer layer to be supported bythe more solid inner layer upon heating and inflation of the balloon. Assuch the outer layer can be changed structurally so as to incorporateadditional components or features into the balloon, whilst the innerlayer maintains the physical characteristics required by the balloonsuch as burst strength and compliance. In such a way additionalcomponents may be incorporated into a balloon in an easy and effectiveway without compromising the physical characteristics of the balloon.The inner layer acts to provide support to the outer layer, both duringthe manufacture of the balloon and also during subsequent deployment ofthe balloon in a medical procedure.

In some embodiments the second layer of the balloon comprises a softlayer. By soft it is meant that the layer may deform around an elementor device, such as a stent, pressed into it. The second layer remainsrelatively soft after manufacture of the balloon such that an element ordevice may be partially embedded into the soft layer after manufactureof the balloon. In one embodiment, a stent is crimped into the softlayer, partially embedding the stent into the soft layer and thusattaching the stent to the balloon. The soft layer is thicker than thefirst layer in order to provide sufficient thickness for the stent topartially embed. For example, the soft layer may have a thicknesssubstantially equal to the thickness of the stent strut.

The skilled person would appreciate that modifications could be made tothe above-described embodiments. Any compatible materials could be usedfor the two layers (for example, two hydrophobic layers or twohydrophilic layers), as long at the material for the inner layer has ahigher melting temperature than that of the outer layer. Furthermore, itwould be possible to combine a hydrophilic layer with a hydrophobiclayer by chemically linking the layers or including a middle “tie” layerwith intermediate properties.

The preferred embodiments have only two balloon layers, the layershaving been preferably co-extruded to form the raw tubing used to formthe balloon, or otherwise bonded to one another so as to be integralwith one-another. Other embodiments contemplate more than two layers,for example, three or more, with the proviso that the outer layer of theballoon remains supported by an internal layer which does not melt orflow so as to incorporate additional components at the processingtemperatures. In some embodiments the raw tubing may comprise twoseparate layers, each layer being a separate raw tube. The two separateraw tubes may be provided one inside the other, closely adjacent to oneanother.

Although the claims are set in single dependent form, it is to beunderstood that the features of the dependent claims can be combinedwith one another in accordance with the teachings above, as if theclaims were in multiple dependent form.

All optional and preferred features and modifications of the describedembodiments and dependent claims are usable in all aspects of theinvention taught herein. Furthermore, the individual features of thedependent claims, as well as all optional and preferred features andmodifications of the described embodiments are combinable andinterchangeable with one another.

The disclosures in United Kingdom patent application number GB1205369.0, from which this application claims priority, and in theabstract accompanying this application are incorporated herein byreference.

We claim:
 1. A method of making a balloon, so that said ballooncomprises: an inner layer comprising a first expandable material havinga first softening or melting temperature; an outer layer comprising asecond expandable material including a functionalized polymer, andhaving a second softening or melting temperature that is lower than thefirst softening or melting temperature; wherein the inner and outerlayers are disposed in an overlying and integral or otherwise bondedrelationship with one another; and a woven material or braided mesh thatis at least partially embedded in the outer layer; wherein the innerlayer has a heat-set temperature higher than a heat-set temperature ofthe outer layer, and the inner layer is free of the woven material orbraided mesh and wherein the method of making the balloon comprisessteps of: placing the woven material or braided mesh within a moldcomprising a cavity defined by an internal cylindrical surface;directing a portion of the inner layer and the outer layer, formed asraw tubing, into the cavity; preheating the raw tubing to a temperature,at or above the second softening or melting temperature and below thefirst softening or melting temperature, such the outer layer is softenedto be flowable and the inner layer is soft enough to be expanded, andexpanding, by fluid pressure, the portion of the raw tubing within thecavity such that the expanding places the softened outer layer intocontact with the woven material or braided mesh and where the softenedouter layer is forced flowably into and at least partially through thewoven material or braided mesh so as to at least partially embed thewoven material in the outer layer.
 2. The method of claim 1, furthercomprising a step of further heating to a heat-set temperature of thefirst expandable material of the inner layer.
 3. The method of claim 2,where the step of expanding within the cavity and the further step ofheating to the heat-set temperature of the first expandable material ofthe inner layer provides a burst strength of the inner layer that ishigher than a burst strength of the outer layer.
 4. The method of claim1, further comprising a step of cooling, wherein the woven material orbraided mesh is fixed in the outer layer.
 5. The method of claim 1,where the functionalized polymer comprises a functionalized polyolefin,and the first expandable material comprises nylon.
 6. The method ofclaim 1, where the outer layer comprises material selected from a groupconsisting of polyolefin resin, polyurethane resin, anhydride-modifiedethylene elastomer-based adhesive resin, anhydride-modified linearlow-density polyethylene, a polyolefin modified with hydroxyl groups, apolyolefin modified with anhydride groups.
 7. The method of claim 1,where the second softening or melting temperature is in a range selectedfrom 115° C. to 140° C., 115° C. to 125° C., below 100° C., below 120°C., and below 140° C.
 8. The method of claim 1, where a thickness of theouter layer is in a range selected from no more than 20% of a thicknessof the inner layer and no more than 40% of a thickness of the innerlayer.
 9. The method of claim 1, where the first softening or meltingtemperature is in a range from 165° C. to 205° C.
 10. The method ofclaim 1, where the heat-set temperature of the outer layer is no morethan about 80% of the heat-set temperature of the inner layer.
 11. Themethod of claim 1, where the heat-set temperature of the outer layer isat least 20° C. less than the heat-set temperature of the inner layer,or is at least 10° C. less than the heat-set temperature of the innerlayer.
 12. The method of claim 1, where the inner layer comprises amaterial selected from a polyamide, a polyether block amide, apolyurethane, a polyethylene, polyethylene terephthalate (PET), andsilicone.
 13. A medical balloon comprising: an inner layer comprising afirst expandable material having a first softening or meltingtemperature; an outer layer comprising a second expandable materialhaving a second softening or melting temperature that is lower than thefirst softening or melting temperature; wherein the inner and outerlayers are disposed in an overlying relationship with one anothercombined by a middle tie layer with a melting temperature intermediateof inner layer melting temperature and outer layer melting temperature;and a woven material that is at least partially embedded in the outerlayer; wherein the inner layer has a heat-set temperature higher than aheat-set temperature of the outer layer, and the inner layer is free ofthe woven material.